1. Field of the Invention
The present invention relates to a magnetic recording medium in which a recording layer is formed in a predetermined concavo-convex pattern and recording elements are formed as convex portions of the concavo-convex pattern, a magnetic recording and reproducing apparatus including that magnetic recording medium, and a manufacturing method of that magnetic recording medium.
2. Description of the Related Art
Conventionally, a protective layer is formed over a recording layer in a magnetic recording medium such as a hard disk in order to protect the recording layer against contact with a magnetic head or the like. The protective layer is required to have abrasion resistance and corrosion resistance. For example, a film of carbon called as diamond like carbon is specifically known as a material for the protective layer that meets the above needs, for example. Exemplary methods for forming such a carbon film over a recording layer are CVD (Chemical Vapor Deposition), IBD (Ion Beam Deposition), and bias sputtering, in each of which carbon is deposited over a surface while a bias voltage is applied to a substrate (see Japanese Examined Patent Publication No. Hei 6-60404,for example).
On the other hand, developments such as miniaturization of magnetic particles forming a recording layer, change of a material for the recording layer, and miniaturization of head processing have been made to largely improve areal density of a magnetic recording medium. The improvement of areal density is expected to continue. However, the improvement of areal density by conventional approaches has reached its limit, because many problems such as processing limits of a magnetic head, incorrect recording of information onto a track adjacent to a target track because of broadening of a recording magnetic field of the magnetic head, and crosstalk during reproducing have become remarkable. Thus, in order to further improve areal density, a discrete track medium and a patterned medium have been proposed, in which a recording layer is formed in a concavo-convex pattern and recording elements are formed as convex portions of the concavo-convex pattern.
For a magnetic recording medium such as a hard disk, flatness of the surface of the medium is important in order to achieve a stable flying performance of a magnetic head. In the discrete track medium and the patterned medium in which areal density is high and a magnetic gap is small, flatness of the surface of the medium is especially important and therefore it has been proposed to fill a concave portion between the recording elements with filling elements. It is preferable that the filling elements have high hardness and good corrosion resistance. Specific examples of a material for the filling elements include oxides such as SiO2, nitrides, and carbides.
In order to fill the concave portions with the filling elements, a method can be used in which a filling material is deposited over the recording layer having the concavo-convex pattern by sputtering so as to fill the concave portions and thereafter an excess part of the filling material over the recording layer is removed by CMP (Chemical Mechanical Polishing) or dry etching such as ion beam etching so as to flatten a surface.
For the discrete track medium and the patterned medium, it has been proposed to form a protective layer of carbon over the recording elements and the filling element (see Japanese Patent Laid-Open Publication No. 2000-195042, for example).
When the concave portions between the recording elements are filled with the filling elements, an upper surface of the recording elements and an upper surface of the filling elements are flattened, and then those upper surfaces are covered with the protective layer, it is expected that a flying performance of a magnetic head can be made as favorable as that obtained by a magnetic recording medium in which a protective layer is formed over a continuous recording layer.
However, even if the discrete track medium or the patterned medium has the same level of surface roughness as the magnetic recording medium having the continuous recording layer, the same level of the flying performance of the magnetic head as that obtained for the magnetic recording medium having the continuous recording layer is not obtained for the discrete track medium or the patterned medium in some cases. That is, the discrete track medium and the patterned medium have a problem of reliability.